This proposal is designed to investigate the mutagenic properties of B chromosomes in maize. In particular, it is proposed to investigate whether B chromosomes are indeed mutagenic, whether transposable DNA sequences are involved with this putative mutagenicity, and, more specifically, whether Robertson's Mutator system is involved in a somatic leaf-striping phenotype elicited by the presence of 5 or more B chromosomes. The proposed study is tripartite. In the first part, mutagenicity of B chromosomes will be measured by standard genetic crossing techniques utilizing marker stocks. In the second part, genetically mapped mutant alleles that have arisen in a stock with B chromosomes will be compared to progenitor alleles at the molecular level to determine whether they were caused by insertions-of transposable DNA sequences. In the third part of the study, DNA from white and green sectors of striped leaves will be analyzed at the molecular level for redistribution of Mu sequences. In the last two parts of the study information will be obtained via Southern blotting techniques. There is strong circumstantial evidence that B chromosomes may be mutagenic and that transposable elements may be involved with this mutagenicity. If this proves to be the case, the implications for the study of transposable element systems as well as effects of B chromosomes are far-reaching. Alternatively, should B chromosomes prove to be non-mutagenic and should no evidence for transposability of Mu sequences be found, then valuable information on the activity of Mu sequences (which are known to be present on B chromosomes) may be obtained.